The present invention relates generally to excitation circuits, and in particular to a system and method of controlling an excitation circuit during fault conditions.
Aircraft systems often utilize variable differential transformers (VDT's) to measure a linear or rotary position of mechanical equipment such as, for example, the position of a rudder, aileron, valve, or pilot control inceptor. VDT's require a sinusoidal excitation voltage. This excitation may be provided from, for example, electronic equipment that also utilizes the position information from the VDT to control an aircraft system.
Both the electronic equipment and the VDT must be protected in the case of a failure, such as a short circuit between the excitation output and the VDT. Accommodation of these failures is often accomplished by shutting off the excitation circuit. Following shutoff of the excitation circuit, redundant systems of the aircraft take over and allow for continued safe operation of the aircraft.
In prior art systems, upon detection of a failure, the output of the excitation circuit is shut off by turning off a set of electronic switches such as relays, transistors or similar components to disconnect electrical power from the excitation circuit. In this design, all of the electrical current that flows from the excitation circuit to the VDT during normal operation must also flow through the electronic components of the shutoff circuit. In the case of a short circuit fault, all the excess current generated by the short circuit must flow through the electronic components of the shutoff circuit until the failure is detected and the electronic components of the shutoff circuit are turned off. Because of this, the electronic components of the shutoff circuit must be relatively large, high-power devices that require thermal management to prevent them from failing during the short circuit condition. It is desirable to have an excitation circuit that is capable of being shut off during a failure without the need for high-power devices that require thermal management.